Method for firing coal in pyro-processes using direct heat recuperation from a cross flow heat exchanger

ABSTRACT

Coal is placed upon hot mineral solids being cooled by an upward flow of ambient air; the coal is dried, ignited and completely combusted under process conditions associated with cooling after firing. The hot off-gas from cooling is returned directly to the firing section or other sections of the process as heat.

BACKGROUND OF THE INVENTION

Present day energy shortages have spurred activity in industries of alltypes to find methods of utilizing indigenous sources of fuel. The priceof fuel oil and natural gas is increasing and the availability of thesefuels in many areas of the world is decreasing. Under these conditionscoal becomes a viable source of alternate fuel.

In the pyro-processing of minerals for the purposes of agglomeration andinduration, or conducting high temperature reactions, coal must, in thepresent state of the art, be dried and finely pulverized before it canbe used as a fuel. There are high capital, labor, maintenance, thermaland electrical energy costs associated with such preparation of coal foruse as fuel.

The ash contained in the pulverized coal also enters the process andmay, depending upon its specific characteristics, remain unaltered ormelt to form a viscous slag in that portion of the process wherecombustion is occurring. The ash may undesirably contaminate the productirrespective of what occurs during combustion. If the ash is unaltered,it becomes entrained because of its extreme fineness in gaseous productsof combustion and other gases and exits the process as an atmosphericpollutant. If the ash tends to melt, it will also be carried by theprocess gases and adhere to the inner surfaces of the processingequipment wherever the process gas stream impacts. Wherever thisadherence occurs, accretions build by the adhesive ash capturing productdust. The building of such accretions can consume the valuable product,and impair process operations and economics. Presently each process isbest operated with coals having rather specific limits on ash contentand characteristic. The ability of mineral pyro-processing industries toutilize either lowest cost or best available coals is, therefore,restricted.

Wherever possible, mineral pyro-processing employs recuperative productcooling to reduce fuel consumption. If the hot product is non-reactiveand sufficiently dimensionally stable to be cooled in the form of gaspermeable bed, the cooling medium is air. Such cooling is done with aforced upward flow of air with the permeable bed moving either downwardsor horizontally, depending upon the design of the cooler. As the airflows upwards through the bed it removes heat from the bed and leavesthe top of the bed heated to a high temperature.

The hot air leaving the bed is then returned to the process where it isutilized as hot combustion air for combustion efficiency and as asignificant source of process heat.

In an attempt to reduce energy use, many methods have been devised toutilize waste heat from the process system with various degrees ofsuccess. Examples of methods to utilize system heat are disclosed inU.S. Pat. Nos. 2,466,601; 2,580,235; 2,925,336; 3,110,483; 3,110,751;3,313,534; 3,416,778; 3,627,287; 3,653,645; 3,671,027; and 3,782,888.

In U.S. Pat. No. 2,466,601 there is disclosed a method of obtainingthermodynamic balance of heat among various units of a pyro-processsystem.

The aforementioned U.S. Pat. No. 3,313,534 discloses a system includinga two-stage cooler, with preheat air from the first cooler stage passinginto the kiln and the secondary air being discharged to atmosphere aswaste heat, an auxiliary burner over the grate and a bypass is providedfor some of the gas from the kiln to pass directly to the dryingchamber. In such a system, a regulated quantity of kiln gas that has notpassed through material in the preburn chamber may be mixed with gasthat has passed through the material in the preburn chamber and themixture passed through material in the drying chamber. Although thissystem achieves proper thermodynamic balance, it requires more fuel anda kiln about 20 percent larger in diameter than is required for a systemsuch as the one in which the present invention is incorporated, for areason that will appear and be explained as the description of prior artproceeds.

U.S. Pat. No 2,580,235 discloses bypassing preheated air from the cooleraround the kiln and the preburn chambers to drying chambers andadditionally discloses one embodiment in which kiln gas can also bebypassed to a drying chamber without passing through material in thepreburn chamber. However, such systems also require oversized kilns (ascompared to the kiln size required for the about to be described presentinvention) for a reason that will now be explained. Oversized kilns arerequired because at startup and before hot pellets reach the cooler, thecooler provides no heat and all heat needed for the chambers over thegrate must come from the gases passing through the kiln. Accordingly,the kiln must be sized to accommodate that greater (temporary) gas flowuntil hot pellets reach the cooler where some of their heat can berecovered and bypassed around the kiln to the chambers over the grate.

The aforesaid U.S. Pat. Nos. 3,416,778 and 3,653,645 (in addition toU.S. Pat. No. 3,313,534) also disclose burners over a grate for aidingto achieve proper preburning on a grate ahead of the kiln. The burnersover the grate in U.S. Pat. Nos. 3,313,534; 3,416,778; and 3,653,645 canaffect the temperature of gases used for drying but after pellets beginto pass from the drying chamber into the preburn chamber, the preburningoperation utilizes heat which is, therefore, no longer available for thedrying operation. Such systems, therefore, also require oversized kilnsfor overfiring the burners over the grate. Overfiring the above grateburners in the preburn chamber merely to provide excess heat for dryingoperations is undesirable, because in so doing it can heat the upperlayers of pellets in the preburn chamber beyond the preburn desiredbefore the pellets begin to tumble through a kiln.

U.S. Pat. No. 3,671,027 discloses apparatus for transmitting kilnexhaust gas from a preburn section to one chamber of a drying sectionand utilizing heat at a desired or controlled temperature from thecooling zone to the second chamber of the drying section so as tocondition the material in the second chamber. Heat control is dependenton the mechanical point of connection of the conduit which conducts thecooler gases to the second drying chamber along with baffle settings.There is no attempt to utilize a low cost solid fuel as process energy.

In U.S. Pat. No. 3,627,287 there is disclosed a gas supply pipe forsecondary preheating intake air in the throat portion of a clinkercooler in a manner that the gas is supplied directly into the path ofthe preheated upstream flowing to the downstream end of a kiln. Thepurpose is to supply controllable additional heat to the secondary airprior to combustion of the main fuel stream in the kiln and therebycontrol the combustion within the kiln to vary the regional locationwithin the kiln at which hot gas reaches temperatures in excess of thematerial's maximum temperature.

U.S. Pat. No. 3,782,888 is directed to the problems of reducing kilnsize and fuel requirements relative to tonnages of material treated, andproviding controlled thermodynamic balance in such systems by theutilization of air heating means such as an auxiliary burner, at a novellocation.

As can be seen, all of the aforementioned patents disclose variousmethods of utilizing energy either as an addition or as recouped air ora combination of both. All have in common the conservation of high costenergy and attempt to make a more efficient use of the energy required,but none of the foregoing teach adding fuel to the material bed in thecooling zone and utilizing the generated heat in the kiln or final heattreatment zone.

The present invention is directed to the concept of distributingminimally crushed coal or any other solid fuel on the top of the coolingbed when the bed and hot air leaving it are hot enough to cause ignitionand sustain stable combustion. The temperature and heat content of theair leaving the cooler and returning to the process are therebysignificantly increased resulting in a substantial reduction ofpulverized coal consummed in the process. It will be apparent that inthe practice of this invention the cost and energy requirements of coalpulverizing are reduced.

The ash contained in the solid fuel fed to the cooler has not beenreduced to a finely divided state and in the main is incapable of beingentrained in the hot air leaving the bed and being returned to theprocess. This expands any limits imposed on the quantity andcharacteristics of the ash in the solid fuel fed to the cooler withrespect to accretion build up or atmospheric pollution. The effect ofproduct contamination by the coal ash is significantly diminished as itis not dispersed throughout the product but largely segregated to theproduct at the top of the cooling bed. As the ash is of relatively largesize, it is relatively simple to distinguish and remove it from theproduct.

More specifically, the present invention is directed to the concept ofadding coal into the cooler of a pyro-processing system. This, as far asapplicant is aware, has never been undertaken because of fusion effectwhich has always appeared to be a serious impediment which deterredpersons skilled in the art from exploring this method of reducing energyconsumption.

SUMMARY OF THE INVENTION

According to the present invention, provision is made to place coal uponhot pellets being cooled by an upwards flow of ambient air. The addedcoal will be dried, ignited and completely combusted under processconditions normally associated with primary cooling after firing. Thehot gas from the combustion of the added coal is utilized in the firingin the final heat treatment zone or other section of the process. Theadded coal need not be dried, nor does it require to be pulverized, thuseffecting a considerable saving over the method wherein pulverized coalor oil is blown into the firing section.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary diagrammatic view, in vertical section, of apyro-processing system in which the invention is incorporated; and

FIG. 2 is a fragmentary diagrammatic view in section of a straight gratetype of pyro-processing system in which cooling is accomplished by crossflow solids to air heat transfer.

DESCRIPTION OF THE INVENTION

The preferred application of this invention is to mineral pyro-processesin which cooling is accomplished by cross flow solids to air heattransfer. This method of cooling is done in devices that convey a gaspermeable bed in a plane sufficiently horizontal such that there is norelative movement between product particles.

The invention applies to any pyro-process having at least two chambers;one to heat solids to a specific high temperature in an oxidizingatmosphere and the other to cool the solids as a packed or permeable bedby cross flow solids to air heat transfer. The two chambers must beinterconnected so that all or part of the heated air leaving the coolingchamber is returned to the heating chamber for the purpose of returningto the heating chamber a substantial amount of the heat required to heatthe solids.

The temperature of the air returned from the cooling chamber to theheating chamber will be less than the specific temperature to which thesolids must be raised and fuel must be combusted and transmitted to theheating chamber, returning a substantial amount of the heat required forheating the solids.

The hot air returned from the cooling chamber will be less than thetemperature specifically required to process the solids and must beelevated in temperature by the combustion of fuel.

The temperature of the air returned from the cooling chamber to theheating chamber will be less than the specific temperature to which thesolids must be raised and fuel must be combusted to raise thetemperature of the air above.

This invention applies to any pyro-process that has one or more chambersin which fuel is fired for heating material to high temperature and inwhich the heated material is cooled as a packed bed by cross flow solidsto air heat transfer for the purpose of returning sensible heat from thecooling bed to the process to reduce fuel consumption. The purpose ofthe invention is to partially substitute solid fuel of low or randomquality for coals of specific and controlled quality, natural gas orfuel oil required for acceptable operation of the process chambersprovided for material heating.

The heating chambers referred to are rotary kilns wherein materials areheated by flame radiation or external combustion chambers providing hotgas for packed bed, cross flow, gas-to-solids heat transfer as used ontraveling grates. Such chambers are used in iron ore pelletizing in twotypes of processes, the Grate Kiln and the Straight Grate. The travelinggrate is used in both processes. In the Grate Kiln System, it is used todry and preliminarlly indurate iron ore agglomerates sufficiently forfinal high temperature induration in a rotary kiln. In the straightgrate process, the grate is extended to include final induration andrecuperative cooling.

The invention is described as it would be applied to a great kiln systemarrangement as an example of suitable apparatus which would benefit fromthe application of the present invention. However, the invention isapplicable to any pyro-processing system using cooling by cross flowsolids to air heat transfer as previously mentioned.

Raw material is prepared for the apparatus to be described by a suitableagglomerating device which may be, for example, a balling pan or a drum(not shown). A suitable device is shown in U.S. Pat. No. 1,775,313. Afeeder (not shown) deposits the green (i.e., untreated) balls of rawmaterials on a gas pervious traveling grate 1. A housing structure 2 isarranged to enclose a space over grate 1 and has a baffle wall 3suspended from the roof of housing 2 to a predetermined distance abovegrate 1. Baffle wall 3 divides the space enclosed by housing 2 into adrying chamber 4 and a preburn chamber 5. Green balls on grate 1 will betransported through drying chamber 4, then preburn chamber 5 and thendischarged down a chute 6 into an inlet opening 7 of a refractory linedrotary kiln 8.

Rotary kiln 8 slopes downwardly from chute 6 toward a hood 9 thatencloses the discharge end of kiln 8 and defines a passage 10 from kiln8 to a cooler 11. The downward slope of the rotary kiln 8 causesmaterial received from chute 6 to pass through kiln 8, then into hood 9and through passage 10 to the cooler 11.

The cooler 11 is provided with blowers 12 and 13, which may be driven byvariable speed driving motors 14, 15, that blow controlled quantities ofair upwardly through windboxes 16, 17 and then through an air perviousgrate 18 and thence through the material on a gas pervious travelinggrate 19. As indicated by arrows, cool air supplied by blower 13 isblown upwardly through windbox 17, grate 18 into a recoup conduit 35 andhaving a damper 37 for a purpose that will appear from the descriptionto follow. Cool air supplied by blower 12 is blown upwardly throughwindbox 16, grate 18, through the material bed on grate 19, and passage10 into the firing hood 9. A burner 28, which is a source of highquality reinforcing heat, is mounted to project into hood 9 to deliverand burn fuel that raises the temperature of the gas passing into kiln 8to the desired high temperature level required for material receiving afinal heat treatment in kiln 8. In apparatus producing hard pellets ofiron ore, pellets will be heated in the kiln 8 to about 2,450° F.

Gas flow from the gas discharge end of kiln 8, up chute 6, and into thematerial preburn chamber 5 will be in a temperature range of about1,600°-2,200° F.

A conduit means 30 is provided which includes on its first end acollector header 31 which is constructed and arranged to connect with awindbox assembly 32 beneath the grate 1 and preburn chamber 5. Theconduit means 30 has a second end connected to a fan 36, the operationof which passes gas to the chamber 4 by conduit means (not shown). Therecoup conduit 35 is in communication with the interior of the cooler 11at a position towards the material discharge end thereof and is alsoconnected to the conduit means 30. With this arrangement a mix of gaspassing from the kiln 8 into the chamber 5 and recoup gas from thecooler 11 as established by a damper 37 in recoup conduit 35 isavailable to be utilized for purposes such as reinforcing the heat inthe drying chamber 4.

A fuel burner 41 projecting into the recoup conduit 35 may be operatedto reinforce the heat of the air from the cooler 11, if necessary. Ifthe temperature of the recoup gas in conduit 35 is to high, a damper 40is operated to add ambient air to lower the temperature and the outputfrom burner 41 reduced or turned off.

Green balls containing iron ore or iron concentrate are formed in aballing device (not shown) and placed upon grate 1 for transport throughchamber 4 before they are transported into the preburn chamber 5 toavoid pellet break-up and dust formation that could block a flow of gasthrough the bed of pellets in preburn chamber 5. However, during initialstages of startup operations, the auxiliary stack 46 is opened and fuelfrom kiln burner 28 is burned to bring the refractory lined kiln 8 up tooperating temperatures. During this period of startup operation, noheated gas is as yet passing into windboxes 32 and conduit 30 forpassage to drying chamber 4. Likewise, during this period of startupoperation, no hot pellets have as yet arrived in the cooler 11 toprovide heat for transfer to the air from fans 12 and 13 that pass intobypass 35.

As mentioned, the burner 41 is ignited to burn fuel and heat air inrecoup conduit 35, to provide hot air for passage through conduit 30 toan outlet in housing 2 (not shown) above drying chamber 4. The quantityand temperature of the gases entering chamber 4 must be controlled tosatisfy specific requirements of the green ball material in the chamber.Quantity is controlled by throttling the fan 36. Burner 41 may be usedto raise the temperatures of the gases going to chamber 4 or the gasesmay be tempered by ambient air controlled by damper 40 to provide therequired quantity of air at the required temperature. The pellets arethereby properly dried as they pass through chamber 4. The dried pelletspass into preburn chamber 5 and provide a protective cover for grate 1.Fan 36 may be operated to allow hot gases at temperatures over 1,800° F.from the kiln 8 to pass downwardly through the pellets and intowindboxes 32. Pellets in chamber 5 are heated to an average temperatureof about 1,800° F. or higher and the gases which have given up much oftheir heat pass into windboxes 32. Thus, the auxiliary stack 40 and theheat input by burner 41 will be adjusted with respect to the heat andflow available from windbox 32.

After the pellets have been given the desired preburn treatment inchamber 5, the bed of pellets on grate 1 is disrupted and the pelletsare tumbled through kiln 8 wherein they are heated to about 2,400° F.The hot pellets are discharged from kiln 8 and fall through passage 10onto the grate 19 of cooler 11. After the pellets pass through thecooler 11, they are cooled sufficiently for handling and storage.

The gas in the cooler 11, which has been preheated as it passes throughthe pellets on grate 19, passes up passage 10 and into kiln 8. The flameand gases from the reinforcing high quality heat from the burner 28 mixwith the air from cooler 11 to provide an atmosphere in kiln 8 that isover 2,400° F. These high temperature gases move counter to the flow ofpellets through kiln 8 and pass into preburn chamber 5 at over 1,800° F.

Pellets moving from the forward or admission end of the cooler 11towards the discharge end thereof may be at temperatures of 700° to 800°F., and air from fan 13 passing through these pellets recuperates heatfrom the pellets and is heated to temperatures which may be, forexample, in the range of 500° to 700° F. The gas passing through recoupconduit 35 joins with hot gas from windboxes 32. These gases may betempered with ambient air from stack 40 or heated with fuel supplied byburner 41 to provide the temperatures and quantity of gas needed to drythe pellets in chamber 4.

With the apparatus shown, heat requirements during startup operation andafter startup operation are normally provided for by burner 28 and kiln8 as is the practice in this technology. However, it has been found thatthe heat necessary to be supplied to the kiln 8 by the kiln burner 28can be materially reduced. This can be accomplished by a simple methodof firing coal in the forward or admission end of the cooler. To thisend a coal feeder means herein depicted as pipe or conduit 51 isprovided and arranged to communicate with the interior of the cooler 11adjacent the admission end thereof. Crushed coal from a source (notshown) is supplied to the conduit 51 and is spread by distributor (notshown) on the pellet bed moving with the grate 19. This serves to spreadthe coal evenly across the material bed and avoids a heavy pile-up ofcoal in the area of the coal feeder 51. The coal feeder 51 is adapted tofeed about 25 to 40 percent of a process total fuel requirement.However, the coal feed rate may be varied to suit a particularpyro-processing system requirement. The coal placed upon the hot pelletsbeing cooled by an upwards flow of ambient air from the windbox 16 willbe dried, ignited and completely combusted under process conditionsassociated with primary cooling after firing.

The high quality heat in the off-gas from the combusted coal added ontothe material bed in the cooler zone 11 is recouped via passage 10,conduit 56 and recoup duct 35. Conduit 56 at one end 57 communicateswith the interior of the cooler 11. At its opposite end 58, the conduit56 communicates with the passage 10 adjacent the discharge end of kiln 8and above the burner 28 thereby forcing the hot burner and cooleroff-gas downwardly from the top of the hood 9 forcing the gas downwardlyso as to enter the kiln 8 parallel to its centerline. Thus, the off-gasfrom the material bed in the cooler 11 is recouped and directed byconduit 56 into the kiln 8 as a source of high quality heat. This servesto reduce the heat input from burner 28 by 25 to 40 percent of theprocess heat requirement. The end 57 of the conduit is positioned asclose to the area wherein the coal is added onto the bed in cooler 11 toensure that the recouped off-gas will be at the highest temperature.

The end of recoup conduit 35 communicates with cooler 11 at a positionafter and away from the area wherein the coal is added to the coolerbed. This provides a hotter gas for recoup 35 than was previouslyavailable. As a result, the amount of heat furnished by burner 41 can bereduced or discontinued by shutting off burner 41.

This method provides a simple method of firing coal in any pyro-processsystem wherein solids are cooled by updraft, cross feed, solids to gasheat transfer through a packed material bed. Also, the method providesfor recouping the high quality off-gas heat and returns it directly tothe firing section of the process. As a result, the amount of highquality heat to the firing section or kiln 8, furnished by thereinforcing burner 28, can be materially reduced. It is known that theheat furnished by a reinforcing burner, such as burner 28, is obtainedfrom burning gas, oil or coal. If coal is the source for burner 28, itmust be dried, crushed and pulverized so as to accomplish the requiredburning. It is known that drying and pulverizing coal for burning, as inburner 28, is expensive adding materially to the cost of the fuel.

Thus, by adding coal directly onto the hot pellets in the cooler 11,there is obtained a source of relatively inexpensive heat which isusable in the firing section of the pyro-process system; and, the highquality heat provided by the burners 28 and 41 may be reduced providingan operating saving.

The one drawback or impediment to direct firing of pulverized coal,which has been a deterrent in present day iron ore pelletizing, is thatthe ash that is finely divided due to the pulverizing of the coalreadily forms droplets of molten slag which are easily transported byprocess gas. These droplets of slag eventually become deposited in theprocess equipment and cause accretions to build that are a detriment tocontinuous process operation. In the proposed method set forth, the coalsupplied to the cooler need not be pulverized thereby lessening thepotential for ash to be transported by the process gas stream. Thevelocity of the gas leaving the cooling bed is maintained sufficientlylow enough so as not to cause any appreciable entrainment of ash. Thecoal ash which remains with the cooled product in iron ore pelletizingis not detrimental to the product.

Another type of a pyro-processing system utilizing cooling by cross flowsolids to air heat transfer in which the method of the present inventionmay be practiced with advantage is exemplified by the straight gratetype of system 75. The green balls of material are deposited on a gaspervious traveling grate 76. A housing structure 77 is arranged toenclose a space over grate 76 and has a series of spaced apart bafflewalls 78, 79, 80, 81 and 82 which are suspended to a predetermineddistance above the grate. The baffle walls cooperate to define anupdraft drying chamber 86, a downdraft drying chamber 87, first andsecond preheating chambers 88 and 89 and first and second coolingchambers 90 and 91. Exhaust gas from the second cooling chamber 91 isconducted via a connected conduit 96 which includes a fan (not shown) tothe updraft drying chamber windbox 95 in which it is forced or drawn upthrough the material bed on the grate for initial drying.

Exhaust gas from the second preheating chamber 89 is drawn through thematerial bed on the grate into a windbox 97 and directed by a connectingconduit 98 and a recoup fan 99 and utilized for downdraft dryingpurposes in chamber 87. Heat in the second preheat chamber 89 isreinforced by an auxiliary gas fuel burner 101 which serves to raise thetemperature within the chamber.

Heat is also recouped from the first cooling chamber 90 and is directedby means of a header structure 102 into the first and second preheatchambers 88 and 89. The gas passing through the material bed on thetraveling grate through chambers 87 and 88 is drawn into a commonwindbox 103, and, by operation of an exhaust fan 104 is exhausted to acollection system.

The first and second cooling chambers 90 and 91 are supplied withcooling air from beneath the traveling bed from a windbox 106. Coolingair is directed into the windbox 106 by operation of a connected fan107. The heated air passing through the material bed on the grate in thecooling chambers is utilized for updraft drying as previously mentionedand also is directed through the header 102 into the first and secondpreheat chambers 88 and 89.

However, the heat necessary to be supplied to the preheat chambers 88and 89, by the high grade energy burner 101, can be materially reduced.This can be accomplished by the simple method of firing coal in theforward or first cooling chamber 90. To this end, a coal feeder pipe 111is provided and arranged to communicate with the interior of the firstcooler chamber 90. Crushed coal from a source (not shown) is supplied tothe coal feeder conduit 111 and is deposited on the pellet bed movingwith the grate 76. This serves to spread the coal evenly across thematerial or pellet bed and avoids a heavy pile-up of coal in the area ofthe coal feeder 111. The coal feeder 111 may be operated to control thecoal feed rate as desired to suit the particle pyro-processing systemrequirement. The coal placed upon the hot pellet by the coal feeder 111being cooled by an upwards flow of air from the windbox 106 will bedried, ignited and combusted under the process condition associated withprimary cooling after firing. Thus, the off-gas from the material bedwill be recouped and directed by the header 102 into preheating chambers88 and 89 as a source of high quality heat. This will serve to reducethe operation of burner 101, which burns high cost fuel, to a standbyposition.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of treatingmaterial in a pyro-process system in which the material is processedthrough at least a final heat treatment zone and a cooling treatmentzone in which the material received from the final heat treatment zoneis formed into a relatively level bed and cooled by an updraft of airpassing through the bed, comprising the steps of:A. supplying saidmaterial to said cooling zone at a temperature which will ignite coal;B. adding a quantity of coal particles on top of the material bed in thecooling zone, with at least a major portion of the particles being of aminimum size large enough to remain on the bed with the updraft of airpassing through the bed; C. adjusting the velocity of the updraft airthrough the bed to maintain the velocity of off-gases emerging upwardlyfrom the bed below the velocity required to entrain in said off-gasesmore than a minor portion of ash formed by combustion of the coal on thebed; D. maintaining the coal on the material bed in the cooling zone fora period of time sufficient to burn the coal and heat the off-gases; andE. returning the heated off-gases from the combusted coal and saidmaterial to the final heat treating zone as system heat.
 2. A methodaccording to claim 1 in which step B includes adding the coal onto thematerial bed across the entire width of the moving material bedtransverse to the direction of movement of the material bed.
 3. A methodaccording to claim 1 in which the coal added to the material bed in thecooling zone according to step B is deposited adjacent the area whereinthe material from the heat treatment zone enters the cooling zone.
 4. Amethod according to claim 1 in which the off-gas from the combusted coalin the cooling zone is withdrawn from the cooling zone at a positionadjacent to where the coal off-gas is at its highest temperature.
 5. Amethod according to claim 1 in which the coal that is added onto thematerial bed in the cooling zone is crushed coal.
 6. A method accordingto claim 1 in which the quantity of coal added to the material bed inthe cooling zone will supply approximately 25 to 40 percent of apyro-process system total fuel requirement.